1. Field of Invention
The present invention generally relates to a casing with a metallic sheet and a screw adapted to seal a reserved hole of the metallic sheet, and in particular to a casing with a metallic sheet and a screw capable of sitting flush with the metallic sheet when placed in a reserved hole of the metallic sheet.
2. Related Prior Art
With the rapid development of computer technology, the need to add a new component in a computer host (or a server) is increased as time goes by. To meet this demand, the computer casing in which reserved holes are formed therein is frequently used in practice so that a new component can be then installed in the computer casing via the related reserved hole. However, before mounting of new components, the reserved holes have to be temporarily sealed.
Traditionally, screws are commonly used to seal the reserved holes of the casing before the holes are used. As shown in FIG. 5, a conventional screw 2 has a head 20 much greater than the size of a reserved hole 10 defined in a metallic sheet 1 of the casing. The reserved hole 10 is usually an extruded tapped hole which is generally a hole defined in a sheet with a burred edge formed around the hole and a screw thread tapped in the burr. When the screw 2 is inserted into the reserved hole 10 of the metallic sheet 1, the head 20 of the screw 2 is undesirably blocked outside the metallic sheet 1, as depicted in FIG. 6, and therefore spoils the appearance of the casing.
Referring to FIG. 7, countersink screws 3 are selected to fill up reserved holes 31 in the metallic sheet 1 of the casing. It should be noted that the head 30 of the countersink screw 3 is with flat outer face and tapering inner face allowing it to sink into the material. Likewise, the reserved holes 31, also known as countersinks, are formed from a preformed extruded tapped hole and further processed to include the top conical part enlarged so that the countersink screws 3 will fit into the reserved holes 31 and lie below the top surface of the metallic sheet 1, as depicted in FIG. 8. The combination of countersink screws 30 and the countersink 31 improves the appearance of the casing; however, the cost for processing such a countersink is relatively higher.
Referring to FIGS. 9 and 10, grub screws 4, generally fully threaded and headless, are selected to seal the reserved hole 10, namely the extruded tapped hole, in the metallic sheet 1 of the casing. However, without a head, the grub screw 4 might easily be driven out of the extruded tapped hole 10 and fall from the metallic sheet 1 under excessive rotation by an electric tool. Thus, it is quiet inconvenient for users.